A spiral membrane module generally has a structure such that a plurality of spiral membrane elements are connected and received in a pressure vessel (See, for example, Patent Document 1). This separation membrane element has, as a basic structure thereof, a structure such that a single or a plurality of laminates of separation membrane units made of a two-folded membrane leaf having a feed-side channel material sandwiched on the separation layer side of the membrane and a permeate-side channel material adjacent thereto are wound around a center tube having holes.
FIG. 20 shows a cross-sectional view of an element connection part of a conventional separation membrane module. As shown in this Figure, telescope prevention members 36, 37 are installed at both ends of a separation membrane unit 32. An FRP (outer cladding material) 31 is wound on the outside of the separation membrane unit 32. The FRP 31 is made integral with the separation membrane unit 32 and the telescope prevention members 36, 37 by being hardened.
Hub plates 36a, 37a are installed in the telescope prevention members 36, 37, respectively. In actually performing the fluid separation, a force deriving from the pressure difference between the feed side and the concentration side thereof acts in a direction from the feed side to the concentration side of the separation membrane element. This force is held by the telescope prevention member 36 installed on the concentration side. This prevents the separation membrane unit 32 from generating a telescope phenomenon. Further, the above-described telescope prevention member 37 has also a function of holding a supplied liquid sealing member 38. The supply liquid sealing member 38 seals a gap between the pressure vessel 39 and the FRP 31.
In the case of connecting the separation membrane units 32 with each other in series, a coupler 34 serving as a connection tube capable of being inserted into a center tube 33 is inserted into the center tube 33, whereby the two are connected. An O-ring 35 is installed respectively on the inner circumferential surface near both ends of the center tube 33. Also, an annular groove 40 capable of holding the above-described O-ring 35 is installed near both ends of the coupler 34. A separation membrane module having this structure reduces the telescope phenomenon.
However, since the separation membrane elements are not fixed to each other, a relative displacement is generated mutually in the axial direction at the time of start and stop of the operation, whereby the O-ring 35 is liable to slide on the inner surface of the center tube 33. Since this results in the abrasion of the O-ring 35, leakage is generated from the feed side to the permeate side, thereby inviting a risk of contaminating the water quality. Also, since the inner radius r of the coupler 34 is smaller than the inner radius R of the center tube 33, the coupler 34 acts as a resistance against the flow of the transmitted liquid. As a result thereof, there arises a problem of large pressure loss of the permeate-side channel.
In order to solve such a problem, Patent Document 2 described below discloses a connection structure of elements that can compress the O-ring by holding the O-ring on the abutting surface at the end parts of the center tube and installing an engagement part in the hub of the telescope prevention member (cap) so as to fasten the elements with each other. With this connection structure, the abrasion of the O-ring can be prevented by preventing the relative displacement between the elements, whereby the pressure loss in the permeate-side channel can be reduced.
However, with this connection structure, there is a need to prevent loosening of the engagement part due to the pressure change or the like caused by the start or stop of the operation. This raises a problem in that, according as the engagement part of the telescope prevention member is made less liable to be loosened, the operation of the engagement connection or the operation of the connection release will be more cumbersome.
Patent Document 1: Japanese Patent Application Laid-Open Publication No. H11-267469
Patent Document 2; Japanese Patent Application Laid-Open Publication No. 2004-536703